The present invention relates to a wear resistant hard metal free of tungsten carbide and containing mixed carbides of molybdenum carbide and a carbide of a further transition metal as well as a metal or an alloy of the metals from the iron group of the Periodic Table of Elements as a binder metal.
Hard metals comprising of hard transition metal carbide and a ductile binder metal have been known and commercially available for several years. They are used mainly as tools for material working, particularly for cutting work, for stone processing or for noncutting shaping, and also in the area of wear protection. A very high percentage of these commercially available hard metals has tungsten carbide as the major component, sometimes with additions of titanium carbide, niobium carbide or tantallum carbide and cobalt as the binder metal. Tungsten carbide is preferred due to its mechanical properties, namely high hardness, very high modulus of elasticity, and high compressive strength, and also due to its excellent wettability and its high-temperature dependent solubility in the liquid cobalt binder.
Over the years, a technology has been established which permits the reproducible manufacture of hard metals having certain specific properties by changing the state of the starting materials, the manufacturing parameters and by the use of additives. However, it has been and is still difficult to introduce new materials into this established technology.
Recent studies concerning the exhaustion of supplies of certain raw materials have indicated that for some elements there are only very limited minable reserves and that for other elements the majority of the supplies are concentrated in only a few countries. The use of these raw materials may lead to dependencies which may become a risk, particularly for highly industrialized nations. One of these raw materials is tungsten, which has a relatively high specific weight and is not very plentiful.
It has been proposed to produce a hard metal utilizing titanium carbide as the hard substance and nickel as the binder metal, and to improve the wetting behavior between this hard substance and binder by adding molybdenum carbide. Particularly fine grained hard metals were obtained from (Ti,Mo) (C,N) mixed phases. However, the additions of molybdenum carbide were limited. As can be seen from the phase diagram for the molybdenum-carbon system, there exist four binary molybdenum carbides. Of these, only Mo.sub.2 C is stable over the entire temperature range. Mo.sub.2 C, however, is not very hard, is brittle and, moreover, converts to an ordered orthorhombic modification at temperatures around 1700.degree. K. Therefore, binary molybdenum carbides do not offer promising possibilities for industrial utilization as hardness carriers in hard metals.
The situation is different, however, with the ternary molybdenum-tungsten carbide which is rich in molybdenum and with which a (W,Mo)C mixed crystal can be obtained and processed. Molybdenum contents up to 60 Mol % seem to be possible with this system. It has been shown that in the presence of the binder metals iron, cobalt, or nickel, the nucleation of the (Mo,W)C mixed crystals is substantially improved and it has been proposed to produce hard metals by simultaneously melting or sintering for extended periods MoC+WC+Co mixtures.